Children who have cerebral palsy (CP) and spastic diplegia tend to walk with great difficulty and expend considerable energy. An ankle foot orthosis (AFO) is often chosen as the first means of treating these children. However, there are no accepted objective criteria for the prescription of AFOs: their efficacy is controversial, and their cost is not trivial. The long term goal of this research is to improve the mechanics and therefore the gait of children with CP by the application of appropriate AFOs. The apparent benefits of the AFO are: to control undesirable motions, to stabilize weak muscles, and to reduce abnormal muscle tone. We theorize that the AFO controls the ankle joint torques, and these effects propagate up the legs to the proximal joints. We hypothesize that for a child with spastic diplegia the standard and dynamic AFOs, when compared to wearing shoes alone, will: (1) produce a more normal joint torque profile; (2) facilitate more normal muscle activation patterns; and (3) increase efficiency (as measured by V02 consumption). We further hypothesize that the relative efficacy of standard versus dynamic AFOs to enhance locomotion can be tested with the above three dependent measures. Upon completion of this project, the following specific objectives will have been realized: approval or disapproval of the first three hypotheses; establishment of objective criteria to base prescription of standard and dynamic AFOs; validation of gait analysis as a decision-making tool for treating children with CP; and identification of underlying causes of neuromuscular disability, rather than merely documenting effects. We will analyze 36 children under each of three conditions: with shoes alone; with standard AFOs; and with dynamic AFOs. A repeated measures crossover design with an analysis of variance will be used. Computer assessment of both posture and gait will be made. To quantify improvement in function we will measure spatial, kinetic and EMG variables using a 3D dynamic gait analysis system, while V02 will be measured to assess energy efficiency.